The Blue Note is a note in a melody that is outside the usual scale and gives the melody a blues-like character. Blue notes often occur in Jazz and Folk music and most of the music styles that have arisen in America. Their origin lies in African pentatonic music.

Unlike European music, African music does not have a division into whole and semitones, but uses seven steps of approximately the same size, which are slightly smaller than a whole tone. The black musicians in the USA tried to realize this scale on European instruments by striking both the minor and major third simultaneously on the piano or bending the strings on the guitar while playing so that the note was plucked between the minor and major third. This tone, which sounds like a „sigh motif“ to the ears of white musicians – which the singers also intone with their voice – is known as Blue Note. The liminoid character of the Blue Note is obvious, as this tone lies exactly between two tones that are valid in occidental tradition. The bending of the strings (which characteristically also changes the pitch) gives the Blue Note an additional, somewhat indeterminate effect: it oscillates and swings back and forth between the actual notes.¹⁾

Blue Notes are between a quarter and a half tone step „lower than expected“ for Western listeners used to Western harmony. Therefore they can not be used for the formation of chords, as the blues musician Big Bill Broonzy (1903– 1958) stated:

When my song sounds good to me and for me to really sing the old blues that I learned in Mississippi I have to go back to my sound and not the right chords as the musicians have told me to make. They just don't work with the real blues … the blues didn't come out of no book and them real chords did …²⁾

When included as additional notes in a major scale, Blue Notes can be roughly understood as a small third, diminished fifth and small seventh to the root note. However, for the practice of playing, the blues scale is created by adding a diminished fifth to a pentatonic minor scale. This creates a deliberate ambiguity in the gender of the melody, which is interpreted as melancholy from „a non-black point of view“;³⁾ however, blues is originally „a lamentation free of melancholy.“⁴⁾

On the ukulele, blue notes can be developed to a „normal“ (diatonic) note by bend or slide.